Ice has been produced and used for many years for cooling and refrigeration purposes, such as air conditioning, food processing and preservation and in many industrial processes and operations. The ice produced for such purposes is often in block or similar large forms, or in the form of an aqueous slurry containing ice crystals.
Cox U.S. Pat. No. 4,003,213 discloses apparatus and methods for producing an aqueous ice slurry by utilization of the triple point of water. The triple point of water is the pressure at which ice, water and vapor are in equilibrium. This pressure has been determined to be about 4.6 millimeters of mercury absolute pressure.
According to the Cox U.S. Pat. No. 4,003,213, water is fed into a vessel having a pressure slightly below the water triple point pressure. Vapor formed in the vessel is continuously removed as it is formed. The continuous removal of water vapor from the interior of the vessel upsets the equilibrium which is restored by the vaporization of additional feed water. The heat required for vaporization is extracted from the water itself but as the water is already at its freezing point the removal of vapor also causes a remaining portion of the water to freeze. Thus, water is continuously and simultaneously boiling and freezing within the vessel. The heat removed to freeze 1 pound of ice is equal to 144 BTU, the heat of crystallization of water. The thermal energy required to vaporize 1 pound of water is about 1073 BTU. The ice crystals formed in the vessel are removed with water as a slurry mixture.
The vapor produced in the vessel is condensed, in one embodiment, in an antifreeze solution chilled by an evaporator coil external of the vessel. The antifreeze solution becomes diluted and is reconcentrated by passage over a hot condensing coil causing dissolved water to be evaporated. It is undesirable, however, to remove the vapor and condense it external of the vessel. The specific volume of the water vapor at the triple point is very large. The pressure drop in the large vapor ducts between vessels would reduce the coefficient of performance of the system. The evaporation process also requires the addition of considerable energy. This (Cox) process for producing ice has a low coefficient of performance.
Engdahl U.S. Pat. No. 4,735,641 also discloses a freezer vessel which is particularly useful for producing ice at the triple point of the solution.
Even though the prior art discloses freezer vessels there is still a need for an improved freezer vessel which provides a large surface area in the freezing section and which permits vapor to leave the liquid surface at a slow velocity so as to make it possible to reduce carry over of feed liquid droplets into the coolant solution. The carry over of liquid into the coolant substantially reduces the system coefficient of performance and contaminates the coolant.